Double-walled body for hot gases or vapors under superatmospheric pressure



May 3, 1949. E. vlLLlGER DOUBLE-WALLED BODY FOR HOT GASES OR VAPORS UNDER SUPERATMOSPHERIC PRESSURE Filed Aug. 21, 1945 I'rmenmrV Eug en Villiger /Patented May 3, 1949 DOUBLE-WALLED BODY FOR HOT GASES R VAPORS UNDER SUPER/ATMOSPHERIC PRESSURE Eugen Villiger, Zurich, Switzerland, assignor to Aktiengesellschaft Fuer Technische Studien, Zurich, Switzerland, a corporation 'of Switzerland Application August 21, 1945, Serial No. 611,876 In Switzerland October 20, 1944 4 Claims. (Cl. 13S-64) l This invention relates to a double-walled body, such as a double-walled tube for conveying hot gases and vapours under pressures higher than atmospheric pressure and in which a space between the inner and outer walls is lled with heat insulating material and means for an equalisation of the pressure between the space filled with insulating material and the space within the inner body are provided. I

If the double-walled body' be constructed for example, as a double-walledtube, the inner tube,

which assumes approximately the same temperature as the medium flowing through t, has, as is well known, to convey the current of steam or vapour, while the outer tube, the temperature of .which is kept by the insulating layer at such `ra height that the properties of its material, particularly its strength, are not impaired thereby;

has to withstand the pressure of the medium flowing through. Such a separation .of the two functions, namely the conveyance of the flowing medium and the resistance to pressure, by using two constructional parts separated from each other by an insulating layer, can only be achieved, seeing that the strength of the inner tube de'- creases greatly as soon as it is highly heated, if provision be made for an equalisation of pressure between the annular space filled with heat insulating material between the inner and outer tubes and the interior of the inner'tube itself. This has been accomplished by the provision of a sufficient number of holes in the walls of the inner tube.

If the medium flowing through such a doublewalled tube with a lpressure balanced inner tube, is subjected to greatly varying pressures, a large number of pressure equalising holes must be provided in the inner tube and the holes themselves must also be of comparatively large size. If the.

holes be too small they give rise to an undesirable throttling or damming action when rapid fluctuations of pressure occur in the current of gas or vapours, so that the rapidly fluctuating pressure' cannot propagate itself with sufficient rapidity throughout the annular space between the inner and outer tubes throug he small holes; The result of this is that t e hot inner tube is subjected to just those Very stresses which it is intended to avoid.

If the holes in the inner tube be made large enough the equalisation of pressure can,y of course,

take place with sufcient rapidity, but there is then the risk that insulating material will be dragged through the holes and into the inner pipe by the medium flowing through the latter. For most purposes, such contamination-of the flowing medium would not be permissible.

In order that the pressure equalising openings in the inner tube can be as large and as numerous `the pressure equalising holes into the interior 2 as is required and at the same time to prevent the medium flowing through the inner tube from dragging the insulating material with it and to ensure also that the equalisation of pressure in the space filled with insulating material can take place likewise comparatively rapidly, it is also known toconnect to the pressure equalising holes in the inner tube, finely perforated pressure egualising ducts or tubes which extend into the insulating layer. pressure equalising tubes make it impossible for any insulating material to be dragged through of the inner tube, and ensure at the same time an equalisation of pressure with comparative ray pidity. Experience has however shown that such pressure equalising tubes make the uniform or sufficiently dense filling of the space between the inner and outer walls with insulating material tubes and the inner wall cannot be utilised for the insulation of heat flowing from the equalising tubes towards the outer wall of the double-walled body. The result of this is that those places on. the outer wall of the double-walled body which are nearest to the pressure equalising tubes be come comparatively hot which is undesirable for the reasons given above.v

In order to overcome the last mentioned draw backs, according to the present invention a double-walled body of the kind hereinbefore referred to is provided on the outside of the inner body with at least one hollow space further bounded by an intermediate body which ts closely to the insulating material filling a space between said intermediate body and the outer body. This hollow space on the outside of the inner body communicates both with the space within the inner body through at least one pressure equalising hole in this body and with said space filled with isolating material through at least one pressure equalising hole in said intermediate body.

Constructional examples of the subject matter of the invention are shown in the accompanying drawings in which:

Fig. 1 is a longitudinaisection through a double-walled tube according to this invention.

Fig. 2 is a section on the line II-lI of F18. 1. Eig. 3 isl a-cross section through a second, and

Fig. 4 a. cross section through a third construc- The sieve-like walls of suchk tional form of a double-walled tube 'according to this invention.

In Figs. 1 and 2 of the drawing, I denotes a sieve-like perforated part and 2 an unperforated part of the inner tube of a double-walled tube which is used to convey a heated medium under a pressure greater than atmospheric pressure, e. g. air heated above 750 C. The holes in the part I are denoted by the reference numeral 3. In comparison with the unperforated part 2 this part I is comparatively short. The two parts I and 2 which have to convey the hot air consist either wholly of heat resisting (hammer scale proof) material or they are provided on the inside with a coating of such a material. A space 4 is pro-v vided between the adjoining ends of the two parts I, 2 so that the latter can expand freely longitudinally. 5 denotes the outer pipe of the doublewalled tube the function of which is to withstand any pressure stresses which may occur. Between the inner tube I, 2 and the outer tube 5 an intermediate tube coaxial'with them is provided, the diameter of this intermediate tube being only slightly larger than that of the inner tube. This intermediate tube is composed of an unperforated upper part 6 and a lower part 1 provided with numerous holes l1. A space Il between the adjoining ends of the parts 6 and 'I enables these latter likewise to expand freely longitudinally.

In the double-walled tube described there is a hollow space 9 von the outside of the inner tube I, y2; the space 9 extends longitudinally of this inner tube and is bounded directly thereby and by the intermediate tube 6, l. In this arrangement the unperforated part 6 of the intermediate tube surrounds the perforated part I of the inner tube and theperforated part I of the intermediate tube surrounds the unperforated part 2 of the inner tube. The space between the intermediate tube 6, l and the outer tube 5 is filled 40 with a heat resisting, heat insulating material I0, such as asbestos, glass wool, or hardburnt kieselgur stone. `This space is also made of such dimensions that the highest temperature to which 1 said tube; a iiow directing internal tube spacedl the outer tube 5 is subjected lies still below the 4 limit of temperature at which, if it be exceeded, a. sudden impairing of the strength of the material would occur. The intermediate tube 6, 'l fits closely against the insulating material IIJ. In this arrangement the hollow space 9 between the tubes I, 2 and 6, I communicates through the holes 3 in the part I of the inner tube with the space within the inner tube l, 2 and through the holes 'Il in the lower part 'l of the intermediate tube with the space between the intermediate tube 5, I and the outer tube 5, Between the spaces in question there is set up therefore under all fluctuations in the pressure of the medium flowing through the double-walled tube, due to the nu-4 merous holes 3 in the part I of the inner tube and thernumerous holes 'I1 in the part 'I of the intermediate tube, a very rapid and practically perfect equalisation of pressure, so that neither the inner tube I, 2 nor the intermediate tube 6, 1 is subjected to pressure strains. On the other hand no secondary flow which might be capable of dragging insulating material through the holes 11 and give rise to thermal losses, can take place either in the intermediate space 9 or in the space filled with the insulating material I0.

The perforated intermediate body need not necessarily be cylindrical. Thus the intermediate tube Il of the constructional form shown in Fig. 3 is polygonal in cross section, the sides thereof .being tangential to the cylindrical inner tube I2,

which is provided in the same manner as the Dart I of Fig. 1 with holes over a comparatively short part of its length, so that in the vicinity 0f the corner edges I3 of the perforated intermediate tube II hollow spaces Il are formed on the outside thereof which extend longitudinally of the inner body I2.`

As shown in Fig. 4 a number of perforated bodies I8 which form channels Il may be attached to the outside of an inner tube I5 having holes I6 in it. Thesebodies I9 bear by means of their external surfaces against the insulating material I9 which lls the annular space between the perforated inner tube I5 and the outer tube 20 of a doublefwalled tube. Each channel I1 vcommunicates through at least one coordinated pressure equalising hole I6 with the space within the inner tube I5 and through pressure equalising holes 2| with-the annular space lled with said material I9,

The number of holes to be provided in the inner body and in the intermediate body depends entirely on their size.

What is claimed is:

1. In a conduit for confined ilow of high temperature gaseous pressure fluids, the combination of a pressure resisting external tube, formed of a material whose physical properties would be impaired at the temperature of the fluid to be conveyed; a pervious heat insulating lining within from, said lining within the same; and means forming-at least one rigid-Walled hollow interspace aiordinga dead gas space of substantial volume between said internal tube and the internal surface Qffsaid lining, said interspace being in restricted communication with the interior of the internal'tube and with the pervious body of said lining at pointsrelatively so remote and so chosen with reference to the ilow through the internal tube that said flow cannotinduce sustained flow through the interspace.

2. The combination defined in claim 1 in which there is a single annular interspace which surrounds said internal tube, the latter being ported in a limited longitudinal area to afford communication from the' internal tube to theinterspace,

communication between the interspace and the lining being limited to other portions of the length 'of said interspace.

3. The combination defined in claim 1 in which the internal tube is formed with a longitudinal expansion joint and is mechanically connected at its ends with said external tube.

4. The combination defined in claim 1 in which a plurality of interspaces, arranged in circular series aroundthe internal tube, extend longitudinally along the 4internal tube.

EUGEN VILLIGER.

"REFBENCES CITED Unrrnp STATES -PATENTS 

